1. Field of the Invention
The present invention relates to an optical fiber ferrule holding plate suitable for polishing an optical fiber end surface and method for polishing the same.
2. Description of the Related Art
There have been proposed many optical fiber end surface-polishing apparatuses. Optical fiber polishing apparatuses are configured to hold an optical fiber ferrule in an optical fiber ferrule holding plate, and cause relative movement based on a circular motion between a polishing board and the distal end of the optical fiber ferrule, thereby polishing the distal end of the optical fibers.
A typical ferrule holding plate which can be used in the optical fiber end polishing apparatus stated above is illustrated in FIG. 1. FIG. 1 is a cross-sectional view showing the details of a ferrule holding plate 3 with a single optical fiber attached. Holding plate 3 includes a ferrule receiving cylindrical bushing mounting member 8, which includes a through hole 7 through its center. Ferrule 5 is inserted through hole 7. An external screw thread 8A is provided on the outer periphery of mounting member 8. A box nut 9 is provided with a slit 10, and has an internal thread which engages with the external thread 8A so as to tighten and fit the optical fiber and ferrule onto the cylindrical bushing mounting member 8. As illustrated in FIG. 1, the distal end of ferrule 5 with optical fiber 6 contained therein must be aligned at a predetermined inclination angle to the axis of rotation of the polishing material 11. During polishing operations the end face of the ferrule to be polished is pressed perpendicularly against the polishing surface 11, and the ferrule is rotated to the left and right around its own axis. The polishing surface is indented by the pressure of the ferrule, so that the end face is polished almost spherically in accordance with the curvature of the indentation in the polishing surface. The radius of indentation in the polishing surface, and hence the curvature of the polished end face, can be adjusted by the pressure on the ferrule during polishing. It is well known that the squareness or an error in the tilt angle of the end surface of a polished ferrule with an optical fiber, with respect to a central axis seriously affects the connecting performance of the optical fiber connector. Therefore, it is necessary to set a constant relative distance between the end faces of ferrules and the polishing surface to prepare precise convex-curved surfaces uniformly. A ferrule extending too far beyond the surface of its holding plate has a tendency to wobble which seriously affects the required preciseness of the convex curved surfaces. This problem is further exemplified when the ferrule holding plate is utilized during hand polishing operations. The typical ferrule holding plate, as described above, has a flat base surface 1. For proper hand polishing the ferrule end face should extend a sufficient distance beyond base surface 1 of holding plate 3 so as to deform the polishing surface. The extent of the deformation is determined by the requirements of the particular application. During polishing, base surface 1 of the holding plate 3 will come into contact with the polishing surface 11. In fact, the holding plate 3 will come into contact with the polishing surface 11 even when the holding plate is utilized during machine polishing operations. When polishing an optical fiber end the bottom surface of the holding plate wears down and releases debris as it contacts the polishing material. This debris contaminates the polishing material and reduces the quality of the polished fiber end face. Also, holding plates that lock a ferrule in place do not allow the ferrule to float or back off as the holding plate wears. This in turn will cause an increase in pressure between the end face of the fiber and the polishing material which will ultimately damage the end face of the fiber. Another problem associated with the flat base type holding plates described above is their inability to measure the degree of degradation or wear on the holding plate. If the pressure to the holding plate is applied unevenly during use, the plate may ware unevenly. This will affect the required perpendicularity relative to the polishing material for Physical Contact (PC) and Ultra Physical Contact (UPC) connectors or the 8 degree angle for Angled Physical Contact (APC) connectors. This uneven wear reduces the operating life of the holding plate and also affects the quality of the fiber optic end face.
It is an object of the present invention to provide an optical fiber ferrule holding plate for hand polishing optical fibers and for utilization in an optical fiber end polishing machine that is capable of achieving further improvement in durability and workability.
It is a further object of the present invention to provide a ferrule holding plate that will minimize the contact surface between the holding plate and polishing material during polishing thereby reducing the amount of contaminants from the holding plate which will enhance the polishing quality and extend the operating life of the polishing material.
It is still a further object of the present invention to provide a means of measuring the wear of the holding plate for determining if the required orientation of the plate is maintained, and for determining when the holding plate must be replaced.
To this end, a concave optical fiber ferrule holding plate for polishing an end face of an optical fiber is disclosed. The holding plate may be used alone for hand polishing or multiple holding plates may be integrated into a single plate array for use in an optical fiber polishing machine. The circular holding plate comprises a concave interior with one or more concentric wear rings disposed radially inwardly on said interior from the outer periphery of the holding plate to a point surrounding the optical fiber ferrule located in the center. The holding plate contacts a polishing material only at the peripheral wear ring thereby reducing contamination from the material of the holding plate which reduces contamination of the end face of the fiber during polishing. The degree of deterioration of the wear rings can be easily observed to determine when the ferrule holding plate must be replaced. Furthermore, the measuring of the deterioration of the wear rings allows for monitoring of the orientation or tilt of the holding plate, which is required for proper polishing of the optical fibers.